Method for controlling dislocation positions in silicon germanium buffer layers

ABSTRACT

A method for controlling dislocation position in a silicon germanium buffer layer located on a substrate includes depositing a strained silicon germanium layer on the substrate and irradiating one or more regions of the silicon germanium layer with a dislocation inducing agent. The dislocation inducing agent may include ions, electrons, or other radiation source. Dislocations in the silicon germanium layer are located in one or more of the regions. The substrate and strained silicon germanium layer may then be subjected to an annealing process to transform the strained silicon germanium layer into a relaxed state. A top layer of strained silicon or silicon germanium may be deposited on the relaxed silicon germanium layer. Semiconductor-based devices may then be fabricated in the non-damaged regions of the strained silicon or silicon germanium layer. Threading dislocations are confined to damaged areas which may be transformed into SiO 2  isolation regions.

TECHNICAL FIELD

The disclosure generally relates methods for controlling dislocationpositions in buffer layers, such as for semiconductors, such as siliconor silicon germanium buffer layers. The disclosure further relates tomethods for reducing threading dislocation density in substrates formedfrom semiconductors, such as for silicon-based or silicongermanium-based devices.

BACKGROUND

Semiconductor materials, such as silicon germanium (SiGe) and strainedsilicon (Si) based devices, for example, have increasingly gainedattention as candidates for next generation semiconductor devices. SiGeand Si based devices are of interest in addressing issues associatedwith current semiconductor devices which use a silicon channel layerdisposed on a silicon substrate, for example. SiGe and Si based channeldevices have the potential to be used in high speed devices withpotentially higher carrier mobility than current silicon channeldevices.

SiGe channels typically are difficult to grow on silicon substratesbecause of the large lattice constant mismatch between silicon andgermanium. Consequently, current methods employ a quality relaxedsilicon germanium intermediate layer or “virtual substrate” to provide alattice constant that is larger than the underlying silicon substrate(e.g., substrate). For example, a thin Si epitaxial layer under tensilestrain may be grown on top of the “virtual substrate” to be used as theMOSFET channel.

In current applications, for example, a silicon germanium buffer layermay be grown on a silicon substrate by heteroepitaxy through molecularbeam epitaxy or chemical vapor deposition (CVD). The growth conditionmay be such that the silicon germanium buffer layer is in a state ofnear complete strain relaxation throughout the growth process leading toa larger in-plane lattice constant on its surface than the siliconsubstrate. The increased lattice constant may be the result of “misfitdislocations” formed in the relaxed silicon germanium layer. At typicaltemperatures of epitaxial growth and relaxation, such dislocations maycomprise 60-degree type dislocations that move in (111) planes, forexample.

Generally, during the relaxation process, only the misfit segments ofthe dislocation half-loops contribute to the relaxing of the in-planestrain. Consequently, the misfit segments (as opposed, for example, tothreading dislocations) are typically desirable for relaxed bufferlayers. The threading arms associated with each dislocation half-loopare, however, undesirable. The goal of relaxed SiGe buffer layerfabrication methods is to thus maximize ratio of misfit to threadingdislocation density. Moreover, a flat surface is desirable to reduceinterface scattering associated with undulation of the substrateinterface.

Use of graded silicon germanium buffer layers has been investigated asone potential approach to obtain a quality silicon germanium virtualsubstrate. Generally, this involves a SiGe buffer layer with acontinuously graded amount of Ge in the SiGe buffer layer. In the caseof a SiGe layer with a constant composition (i.e., not graded) grown ona silicon substrate, for example, dislocations may nucleate duringgrowth and interact with one another. This interaction inhibitsdislocations from propagating to the substrate edge and may leave alarge number of threading arms on the surface of the SiGe layer.

In contrast, if a graded Ge composition is used, during relaxation ofthe SiGe layer on the silicon substrate, the nucleation of dislocationsacross the surface may be mitigated by reducing the strain accumulationrate. Consequently, the interaction between dislocations may be reducedand the density of threading arm dislocations on the surface of the SiGelayer may be reduced. For instance, for a constant SiGe layer growndirectly on a silicon substrate, the density of threading dislocationsmay be around 10^(8˜9)/cm². In contrast, the density of threadingdislocations in a graded SiGe layer grown on a silicon substrate may bearound 10^(4˜5)/cm². While graded SiGe reduces the threading dislocationdensity, the Ge grading rate may be low, typically at or less than10%/μm. Consequently, this requires a large thickness of graded SiGebuffer layer, which is a drawback because of, among other reasons, theincreased production costs and increased thermal resistance. The thickgraded SiGe buffer layer thus reduces the number of practicalapplications in which SiGe based devices can be used. Moreover, thestrain-relaxed graded SiGe buffer layer generally has a rough surface.

One approach to reducing the threading dislocation density includesemploying a low temperature silicon buffer layer prior to growing asilicon germanium layer. In addition, ion implantation after growing astrained SiGe layer and subsequent annealing has been investigated as apotential solution to reducing threading dislocation density. Generally,these methods function by introducing non-equilibrium point defects inthe layers through a low temperature silicon buffer layer or through ionimplantation and then inducing the clustering of point defects to relaxthe strain. This results in a low density of threading dislocations.These approaches have shown reduced threading density values of lessthan 10⁴/cm².

The above-identified proposed solutions have demonstrated SiGe bufferlayers with reduced threading dislocation density compared to theconstant composition SiGe layer directly grown on silicon substrate.However, the density of threading dislocation is still higher than about1/cm² if the buffer layer is grown on a silicon substrate. Moreover,threading dislocations may be randomly distributed across the entiresubstrate. This random distribution of threading dislocations may resultin deviation of the properties of individual devices formed on thesubstrate. In other words, threading dislocations degrade some devicesformed on the surface of the substrate while others are not.

Ideally, a relaxed SiGe buffer layer has no threading dislocations onthe entire or a significant portion of the surface. However, from adevice fabrication point of view, it is not necessary for the entiresurface of the substrate to be free of threading dislocations. Forexample, in current semiconductor designs, individual devices may befabricated on a substrate and are separated by non-functional fieldoxide or trench isolation regions. These regions may be employed toseparate adjacent devices. Thus, it may be possible to achieve suitableconditions by removing the threading dislocations from the areas of thesurface in which or on which devices are to be built. Consequently, itis desirable to form a relaxed SiGe layer without threading dislocationsat position-controlled regions where the devices are built.

Attempts have been made to control the location of dislocationdistribution by forming patterned silicon mesa structures with andwithout Ge implantation. For example, Fitzgerald et al., Elimination ofDislocations in Heteroepitaxial MBE and RTCVD Ge _(x) Si _(1-x) Grown onPatterned Si Substrates, J. Electronic Materials, 19, 949 (1990)describes a process of fabricating a patterned silicon mesa structureand then growing a SiGe layer thereon. The patterned mesa structurereduces the threading dislocation density by limiting the dislocationinteraction at small growth areas and then allowing the threadingsegments to escape at the mesa edge.

In Watson et al., Influence of Misfit Dislocation Interactions onPhotoluminescence Spectra of SiGe on patterned Si, J. Appl. Phys. 83,3773 (1998), discloses a process of controlling dislocation nucleationduring SiGe layer growth on Ge implanted Si regions that were previouslypatterned before implantation. However, the use of mesa structuresraises complications because the non-planar mesa structure isfundamentally incompatible with planar silicon VLSI technology.

SUMMARY

A method is disclosed for forming dislocations in selected areas orregions of a planar strained silicon germanium layer grown on a siliconsubstrate. The method may also be used for forming dislocations inselected areas or regions of a planar silicon substrate. In one aspectof the method, dislocations may be formed by intentionally damagingselected regions through ion implantation, ion beam illumination, orother energetic beam illumination.

The damaged regions may contain a plurality of dislocation half-loops orfull loops. After an annealing process, the dislocations relax thestrain of the silicon germanium layer by permitting the misfit segmentsto propagate from one damaged region to another. In the damaged region,the dislocation density may be extremely high leading to extensivedislocation—dislocation interaction. The dislocation half-loops with thecorrect Burger's vectors at the outskirts of the damaged regions may befree to move out into the strained film upon annealing. The net resultis that the damaged regions may act as sources as well as barriers/sinksfor dislocation half-loops.

In one embodiment, the method may form dislocations and in particular,threading dislocations, in the damaged or ion implanted regions of asubstrate or overlying SiGe layer. In one aspect the locations of thethreading dislocations may be lithographically defined.

While the method may produce substrates having average threading densityvalues greater than conventional relaxed buffer layers (as measuredacross the entire substrate surface), the density may be concentrated inone or more regions that are not used to create active electronicdevices. The threading dislocation density in these “pristine” orundamaged regions may be as low as the starting silicon wafers. Thedamaged regions where dislocations may be preferentially formed may beused for trench isolation regions or field oxide regions, therebyreducing any potential to waste areas of the substrate.

The overall fraction of the damaged regions using this method may beestimated as follows. The width of the damaged region may be definedusing conventional lithographic techniques to be as narrow as 0.1 μm. Aseparation between the damaged regions may be dictated by an averagemisfit dislocation lengths, which may be on the order of 50 μm orlarger. As a result, the fractional area occupied by the damaged regionsmay be less than 1%.

In one aspect of the process, threading arms may be located at one ormore “damaged” regions, leaving the remainder of the substrate (oroverlying layer) with substantially no threading dislocations. Thedamaged regions may occupy a small fraction of the overall surface areaof the substrate. The damaged regions may be formed into field oxides ortrenches for isolation between devices, thereby avoiding waste of thesurface area of the substrate.

In another embodiment, a thin silicon layer may be grown over thesilicon germanium layer as a nucleation-inhibiting layer. The silicon“capping” layer may prevent nucleation of dislocation loops at a freesurface of the SiGe layer. The process may also be optimized withrespect to other parameters such as growth temperature, thickness, Gecomposition of the SiGe layer, and annealing conditions to preventunwanted nucleation of dislocations in the non-damaged regions of thesubstrate.

In another embodiment, a method for controlling the dislocation positionin a silicon germanium buffer layer includes providing a substrate anddepositing a strained silicon germanium layer on the substrate. Thesilicon germanium layer may then be irradiated at one or more regionswith a dislocation inducing agent. The dislocation inducing agent mayinclude an ion beam, electron beam, other source of radiation. Thesubstrate and the strained silicon germanium layer may then be subjectto an annealing process to transform the strained silicon germaniumlayer from a coherently strained state, i.e., a dislocation-free state,into a relaxed state with dislocations. Dislocations in the silicongermanium layer are preferentially located in the one or more regions.For example, the one or more regions may contain a high concentration ofthreading dislocations while the remaining regions of the substrate aresubstantially free of threading dislocations.

In another embodiment, a method for controlling the dislocation positionin a silicon germanium buffer layer includes providing a substrate andirradiating one or more regions of the substrate with a dislocationinducing agent. Strained silicon germanium is then deposited on thesubstrate. The substrate and the strained silicon germanium layer maythen be subjected to an annealing process to transform the strainedsilicon germanium layer into a relaxed state. According to the process,dislocations in the silicon germanium layer may be located in the one ormore regions.

In still another embodiment, a method of forming an array of quantumdots on a substrate includes providing a substrate and depositing astrained silicon germanium layer on the substrate. One or more regionsof the silicon germanium layer may be irradiated with a dislocationinducing agent. The substrate and the strained silicon germanium layermay then be subjected to an annealing process to transform the strainedsilicon germanium layer into a relaxed state, wherein the relaxation inthe silicon germanium layer forms a dislocation network in the relaxedsilicon germanium layer. Quantum dots are then formed on the dislocationnetwork.

It is thus one object to provide a method for controlling thedislocation position in a silicon germanium buffer layer. It is anotherobject to damage selected regions of a silicon germanium layer such thatthreading dislocations are isolated in the damaged regions. It is afurther object to transform the damaged regions containing the threadingdislocations into field oxide regions and/or isolation trenches. Furtherfeatures and advantages will become apparent upon review of thefollowing drawings and description of the disclosed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a substrate having a strainedsilicon germanium layer thereon.

FIG. 2 illustrates a side view of the substrate and strained silicongermanium layer shown in FIG. 1.

FIG. 3 illustrates a perspective view of the substrate and strainedsilicon germanium layer with a mask located on an upper surface of thestrained silicon germanium layer.

FIG. 4 illustrates a side view of the substrate and strained silicongermanium layer having a mask composed of photoresist, dielectricmaterial, or other material disposed on the silicon germanium layer.

FIG. 5 illustrates a perspective view of the substrate and strainedsilicon germanium layer being irradiated with a dislocation inducingagent (e.g., Ge+ ions). Dislocations are created in one or more regionsof the strained silicon germanium layer by use of the mask.

FIG. 6 illustrates a side view of the process illustrated in FIG. 5.

FIG. 7 illustrates a perspective view of the substrate and strainedsilicon germanium layer with the mask removed. The damaged regionscontain dislocation loops.

FIG. 8 is a side view of the substrate and strained silicon germaniumlayer shown in FIG. 7.

FIG. 9 illustrates a perspective view of the substrate and a relaxedsilicon germanium layer. The misfit segments of the dislocations areshown traveling perpendicular to one another.

FIG. 10 illustrates a side view of the substrate and relaxed silicongermanium layer shown in FIG. 9.

FIG. 11 illustrates a top view of a region of the substrate whereindamaged regions (e.g., lanes) are shown in a substantially perpendicularorientation. The misfit segments of the dislocations are shown travelingin two directions generally perpendicular to one another.

FIG. 12 illustrates a perspective view of substrate having a relaxedlayer of silicon germanium disposed thereon. A top layer, for example,comprising strained silicon or silicon germanium is located on top ofthe relaxed layer of silicon germanium.

FIG. 13 illustrates a side view of the structure shown in FIG. 12.

FIG. 14 illustrates a perspective view of a substrate having a relaxedlayer of silicon germanium disposed thereon. A top layer, for example,comprising strained silicon or silicon germanium is located on top ofthe relaxed layer of silicon germanium. FIG. 14 further illustrates amask located on the upper surface of the top layer.

FIG. 15 illustrates a side view of the substrate, relaxed silicongermanium layer, and top layer shown in FIG. 14.

FIG. 16 illustrates the transformation of the damaged one or moreregions into silicon dioxide isolation regions.

FIG. 17 illustrates a side view of the substrate and associatedstructures of FIG. 16.

FIG. 18 illustrates a perspective view of substrate wherein thenon-irradiated (non-damaged) top layer portion has reduced threadingdislocations.

FIG. 19 illustrates a side view of the structure shown in FIG. 18.

FIG. 20 illustrates a side view of a substrate having a mask disposedabove an upper surface thereof.

FIG. 21 illustrates a side view of the substrate illustrated in FIG. 20being irradiated with a dislocation inducing agent (e.g., Ge+ ions).Dislocations are created in the one or more regions of the substrate byuse of the mask.

FIG. 22 illustrates a side view of the substrate illustrated in FIG. 21with the mask removed. The damaged regions are located in one or moreregions of the substrate that were exposed to the dislocation inducingagent.

FIG. 23 illustrates a side view the substrate illustrated in FIG. 22having a strained layer of silicon germanium disposed thereon.

FIG. 24 illustrates a side view of the substrate having a relaxed layerof silicon germanium. The relaxed layer is formed, for example, bysubjecting the substrate and strained layer of silicon germanium to aannealing process. FIG. 24 illustrates the misfit dislocation segmentspropagating to adjacent damaged regions.

FIG. 25 illustrates a side view of the structure illustrated in FIG. 24having a top layer deposited thereon. The top layer may be formed, forexample, of strained silicon or silicon germanium.

FIG. 26 illustrates a side view of the substrate and associatedstructures wherein the one or more damaged regions are transformed intosilicon dioxide isolation regions. The non-irradiated (non-damaged) toplayer regions of strained silicon or silicon germanium are substantiallyfree of threading dislocations.

FIG. 27A illustrates top and side views of a silicon substrate having anoverlying layer of strained silicon germanium. An array of damagedregions is patterned in the strained silicon layer. Dislocations may beformed in the damaged regions.

FIG. 27B illustrates top and side views the silicon substrate andoverlying layer of FIG. 27A. The silicon germanium layer is in a relaxedstate (e.g., from an annealing process). The strain relaxation causesthe formation of a network of misfit dislocation segments.

FIG. 27C illustrates top and side views of the silicon substrate andoverlying layer of FIG. 27B. A plurality of quantum dots are formed onthe dislocation network to generate a regular array of quantum dots.

DETAILED DESCRIPTION

With reference now to FIGS. 1 through 19, an embodiment of a process isdisclosed for controlling the dislocation position in a buffer layerformed, for example, from silicon germanium (Si_(x)Ge_(1-x)). Of course,the buffer layer may be formed from materials other than silicongermanium. FIGS. 1 and 2 illustrates a substrate 2 having a layer 4 ofstrained silicon germanium disposed thereon. The substrate 2 may beformed from, for example, silicon or some other semiconductor material.In addition, the substrate 2 may take the form of a wafer or the like.The layer 4 of strained silicon germanium may be formed throughmanufacturing processes such as, for instance, molecular beam epitaxyand/or chemical vapor deposition, although the claimed subject matter isnot limited in scope to these particular processes. The layer 4 ofstrained silicon germanium may be formed with no dislocations formedtherein. In addition, the layer 4 of strained silicon germanium may havea substantially flat upper surface. The layer 4 of strained silicongermanium may be grown either in a metastable state or an equilibriumstate at growth temperatures, for example.

FIGS. 3 and 4 illustrate a mask 6 disposed on the strained layer 4 ofsilicon germanium. The mask 6 is used to define pre-defined regions(described in more detail below) that are damaged in a subsequentirradiation step. Any conventional or later-developed lithographictechnique may be employed to form the pre-defined regions. Examplelithographic techniques include photolithography, electron beamlithography, ion beam lithography, nano-imprint methods, andsoft-lithography processes. FIGS. 3 and 4 illustrates a mask 6 disposedon or over the layer 4 of strained silicon germanium. The mask 6 may beformed from, for example, a photoresist, dielectric, or other suitablematerial.

In an alternative process, the mask 6 may disposed away from the surfaceof the strained layer 4 of silicon germanium. For example, the mask 6may be formed from a stencil mask 6.

As seen in FIGS. 3 and 4, the mask 6 includes open regions 6 a andblocked regions 6 b. The open regions 6 a expose at least a portion ofthe layer 4 of strained silicon germanium layer for subsequentirradiation, as described, for example, in detail below.

FIGS. 5 and 6 illustrate a process of irradiating one or more regions 4a of the layer 4 of strained silicon germanium layer with a dislocationinducing agent 8. The one or more regions 4 a may be those regions ofthe layer 4 of strained silicon germanium that are exposed through theopen regions 6 a of the mask 6. The process of irradiating the one ormore regions 4 a damages those regions 4 a to form dislocations 10. Thedislocations 10 are thus preferentially formed in the one or moreregions 4 a of the layer 4 of silicon germanium in this particularembodiment. The dislocations 10 may include dislocation loops.

The dislocation inducing agent 8 may include an ion beam, electron beam,or other energetic radiation source (e.g., electron beam or x-ray)capable of forming dislocations in the silicon germanium layer 4.Generally, the dislocation inducing agent 8 should be capable ofdisordering the lattice of the exposed surface or substrate 2. Forexample, the dislocation inducing agent 8 may include a germanium ionbeam (Ge+ ions). Other examples of ions capable of inducing dislocationsinclude silicon ions, oxygen ions, hydrogen ions, helium ions, neonions, nitrogen ions, carbon ions, and argon ions. Traditional dopantelements such as boron, phosphorous, arsenic, and antimony, may also beused (in either ionic or neutral form). Thus, the dislocation inducingagent 8 may include neutral or non-ionic species, for example. Theregions 4 a (e.g., damaged regions) of the layer 4 of silicon germaniumcontain numerous dislocation loops caused by the impinging dislocationinducing agent 8.

The dislocation loops in (111) planes with <110> directions within thedislocations 10 (as shown, for example, in FIG. 5) propagate andcontribute to strain relaxation at a subsequent relaxation operation.The nature and/or properties of the regions 4 a (as shown in FIG. 4) maybe affected at least in part via the stress level of the silicongermanium layer 4, the geometry of the silicon germanium layer 4, aswell as the structures and/or functionalities of the devices intended tobe built or fabricated. The damaged region may be generally deep withinthe silicon germanium layer 4, at, for example, the interface betweenthe substrate 2 and the layer 4 of silicon germanium (as is shown inFIGS. 5 and 6), or even inside the substrate 2, for example.

FIGS. 5 and 6 illustrate the regions 4 a in the shape of lanes acrossthe surface of the silicon germanium layer 4. The regions 4 a mayinclude a plurality of lanes arranged in an intersecting orientation (asis shown in FIG. 5). Generally, the width of the regions 4 a (e.g.,lanes) may be larger than the critical radius of the dislocation loopsformed therein. The critical radius is defined as the radius at whichformation of dislocation half loops becomes energetically favorable.

The dislocation loops may have a critical radius within the range ofabout 10 nm to about 50 nm. Consequently, the width of the regions 4 amay be greater than about 10 nm and greater than 50 nm, for example, inone particular embodiment. Of course, the claimed subject matter is notlimited in scope in this respect.

FIGS. 7 and 8 illustrate the mask 6 removed from above the surface ofthe silicon germanium layer 4. The mask 6 may be removed prior torelaxing the strained silicon germanium layer 4. In an alternativeembodiment, the mask 6 may be removed after relaxing the strainedsilicon germanium layer 4. As seen in FIGS. 7 and 8, the dislocations 10are contained in the regions 4 a leaving other regions such as theregions 4 b (e.g., non-damaged regions), having little or nearly nodislocations.

FIGS. 9 and 10 illustrate a substrate 2 including a relaxed silicongermanium layer 12. The layer 4 of strained silicon germanium andsubstrate 2 are subject to an annealing process to relax the strain inthe layer 4 of silicon germanium to a relaxed silicon germanium layer12, such as, for example, as illustrated in FIGS. 9 and 10. Theannealing process may then “pull out” dislocation loops and propagatesmisfit dislocation segments 14 from one region, such as region 4 a, toanother region 4 a. The propagation of the misfit dislocation segments14 may therefore release the strain in the layer 4 of silicon germaniumlayer such that the threading dislocations 16 remain inside the regions4 a. This may result in few or even nearly no threading dislocations(e.g., threading arms) in the regions 4 b.

An annealing process may be performed at temperatures ranging from about400° C. to about 1000° C., for example, although the claimed subjectmatter is not limited in scope in this respect. Annealing may proceed atelevated temperatures for a time period, such as, for example, rangingfrom ten minutes to about two hours. It should be noted, however, thatthe claimed subject matter is not limited in scope in this respect. Theannealing process may include a multi-operation or multi-sequenceannealing process where annealing takes place at multiple temperaturesand/or annealing times. The annealing process may take place in anenvironment that is not a significantly oxidizing environment. Forexample, annealing may take place in an annealing furnace or rapidthermal annealing chamber including a vacuum environment or an inert gasenvironment (e.g., Argon or Nitrogen).

The substrate 2 and strained silicon germanium layer 4 may be subjectedto annealing conditions such that nucleation of dislocations at randomsurface sites is reduced or even prevented. One way to reduce randomsurface nucleation is to form a silicon capping layer (not shown) thatmay be grown on the layer 4 of strained silicon germanium layer prior tothe annealing process. The formation of a silicon capping layer may alsobe done prior to damage formation in the regions 4 a.

As seen in FIGS. 9 and 10, the misfit dislocation segments 14 propagatein an intersecting pattern generally perpendicular to one another. Asshown in FIG. 11, a crossing or intersecting pattern may be formed inwhich misfit dislocation segments 14 propagate in two generallyperpendicular directions. The regions 4 b thus contain a network ofintersecting misfit dislocation segments 14 but may be substantiallyfree of threading dislocations 16. The intersecting lanes (e.g.,crossing pattern) as illustrated in FIG. 11 may be formed in separateprocesses, simultaneously, or otherwise. For example, in one process, amask 6 may be used to damage regions 4 a in a first direction. Thesilicon germanium layer 4 is then relaxed (e.g., with an annealingprocess). A second patterning process may then performed either with thesame or different mask 6. The mask 6 may be used to affect or damageregions in a second direction (e.g., substantially perpendicular to thefirst direction). The silicon germanium layer is then relaxed to form aperpendicular network of misfit dislocation segments 14.

In an alternative process, a perpendicular network of misfit dislocationsegments 14 may be created substantially simultaneously. In thisprocess, a one or more masks 6 may be used to damage the silicongermanium layer 4. The substrate 2 and damaged layer 4 of silicongermanium may be subject to an annealing process to relax the silicongermanium in both directions simultaneously. This alternative processmay omit an additional processing operation inherent in a sequentialprocess. However, a sequential process may reduce the dislocationinteraction.

FIGS. 12 and 13 illustrate a process of forming a top layer 20 formed onor over top of the relaxed silicon germanium layer 12. The top layer 20may be formed, for example, from strained silicon or silicon germanium.The top layer 20 may be used to form, for example, a strained siliconchannel layer for semiconductor devices such as, for example,transistors. If strained silicon is used in the top layer 20,Si_(x)Ge_(1-x) may be employed that includes about 20% Ge. Conversely,if strained Ge is used (e.g., for PMOSFET applications), Si_(x)Ge_(1-x)may be employed that includes about 70% Ge. It should be understood,however, that the process is not limited to a specific composition ofGe. Rather, the process may be used with Si_(x)Ge_(1-x) where the Gecomposition ranges from 0% to 100%.

FIGS. 14 and 15 illustrates a mask 22 disposed above the top layer 20.The mask 22 includes an open region 22 a and a blocked region 22 b. Themask 22 may be the same as or different from the mask 6 describedherein. The top layer 20 includes a regions 20 a that are exposed viathe open regions 22 a of the mask 22. Conversely, the blocked region 22b of the mask 22 may be used to form regions 20 b (e.g., non-damagedregions) in the top layer 20 as is described below.

FIGS. 16 and 17 illustrate the transformation of the regions 4 a, 20 ainto silicon dioxide isolation regions 24. This may be done throughseveral processes including but not limited to trench etching and SiO₂deposition, field oxidation, or oxygen ion implantation and subsequentannealing for SiO₂ formation at the regions 4 a, 20 a. For example,oxide regions 24 may be formed using existing processes for shallowtrench isolation. For example, the regions 4 a, 20 a may be etched by,for example, reactive ion etching followed by filling the etched regionwith silicon dioxide. This process generally involves forming a patternwith photoresist or a hard mask after depositing an etch-stop layer suchas silicon nitride. As best seen in FIGS. 17, 19, and 26, the oxideregions 24 (e.g., etched trenches) may be wider than the dislocations 10such that the final structure is substantially free of dislocations 10.The patterned surface may be subject to etching by reactive ions to forma square-shaped groove. The photoresist may then be removed and thesubstrate may be oxidized to form a thin oxide layer. Silicon dioxidemay then be deposited to fill the etched regions. The top silicondioxide layer may then be removed from the top area of the etch stoplayer and the etched regions. The etch-stop layer may be removed.

FIG. 17 illustrates the formation of the silicon dioxide isolationregions 24.

FIGS. 18 and 19 illustrate the substrate 2 with the relaxed silicongermanium layer 12 and top layer 20 interspersed with a plurality ofsilicon dioxide isolation regions 24. The threading dislocations areincluded in the silicon dioxide isolation regions 24. The portions 20 bof the top layer 20 that are between adjacent silicon dioxide isolationregions 24 are substantially free of threading dislocations.Dislocations in the top layer 20 are isolated with the portions 20 alying just above the silicon dioxide isolation regions 24.

FIGS. 20 and 21 illustrate an alternative process for affecting at leastin part, the dislocation position in a buffer layer formed, for example,from silicon germanium. One difference form the process illustrated inFIGS. 1–19 is that the substrate 2 may be damaged prior to growing thestrained silicon germanium layer 4.

FIG. 20 illustrates a side view of substrate 2 with a mask 6 disposed onor over an upper surface of the substrate 2. The mask 6 includes aplurality of open regions 6 a and blocked regions 6 b. As explainedbelow, the open regions 6 a of the mask permit the passage of adislocation inducing agent 8 into regions 2 a of the substrate 2. FIG.21 illustrates a side view of the substrate 2 being irradiated with thedislocation inducing agent 8 (e.g., Ge+ ions). The dislocation inducingagent 8 may include a ion beam, electron beam, or other energeticradiation source capable of forming dislocations in the substrate 2. Forexample, the dislocation inducing agent 8 may include a Ge+ ion beam (asis shown in FIG. 21). The dislocation inducing agent 8 may result in theformation of dislocations 10 in regions 2 a of the substrate (see e.g.,FIG. 22). As seen in FIG. 21, each dislocation 10 may include a numberof dislocation loops.

FIG. 22 illustrates the mask 6 removed away from the now-damagedsubstrate 2. In a next operation, as shown in FIG. 23, a strained layer4 of silicon germanium may be grown on the substrate 2. The layer 4 ofstrained silicon germanium may be formed through conventional processessuch as, for instance, molecular beam epitaxy and chemical vapordeposition. The dislocations 10 formed in the substrate 2 also appear inthe regions 4 a of the strained silicon germanium layer 4. The regions 4b of the strained layer 4 of silicon germanium are substantially freefrom dislocations 10.

FIG. 24 illustrates the substrate 2 including a relaxed silicongermanium layer 12 after undergoing relaxations by, for example, anannealing process to relax the strain of the silicon germanium layer 4.As best seen in FIG. 24, for example, the annealing operation “pullsout” and propagates misfit dislocation segments 14 the pass from onedamaged region to another. A capping layer of silicon (not shown) may begrown on the strained layer 4 of silicon germanium prior to annealing toreduce and/or prevent the nucleation of dislocations in the regions 4 b.

As seen in FIG. 24, the misfit dislocation segments 14 may propagate inmultiple directions (e.g., generally perpendicular to one another).Consequently, a crossing pattern (such as that shown in FIG. 11) may beformed in which misfit dislocation segments 14 propagate in orthogonaldirections, for example. The regions 4 b thus include a network ofintersecting misfit dislocation segments 14. The intersecting lanes(e.g., crossing pattern) may be formed in separate processes,simultaneously, or otherwise. For example, in one process, a mask 6 maybe used to damage regions 2 a of the substrate 2 in a first direction.The layer 4 of silicon germanium may be grown and relaxed (e.g., with anannealing process). A second patterning process may be performed eitherwith the same or different mask 6. The mask 6 may be used to damageregions 4 a of the layer 4 of silicon germanium in a second direction(e.g., substantially perpendicular to the first direction). The layer 4of silicon germanium may then be relaxed to form a perpendicular networkof misfit dislocation segments 14, for example.

In an alternative process, a perpendicular network of misfit dislocationsegments 14 may be created substantially simultaneously. In thisprocess, a one or more masks 6 may be used to damage the substrate 2.The substrate 2 and layer 4 may then be subject to an annealing processto relax the silicon germanium in both directions substantiallysimultaneously.

FIG. 25 illustrates a top layer 20 that may be grown on the relaxedsilicon germanium layer 12. The top layer 20 may be formed, for example,from strained silicon or silicon germanium. As seen in FIG. 25, thedislocations 10 are concentrated in the regions 20 a thereby leaving theregions 20 b substantially free of any threading dislocations.

FIG. 26 illustrates the substrate 2 with the relaxed silicon germaniumlayer 12 and top layer 20 interspersed with a plurality of silicondioxide isolation regions 24. The threading dislocations are allincluded in the silicon dioxide isolation regions 24. The regions 20 bof the top layer 20 that are between adjacent silicon dioxide isolationregions 24 are substantially free of threading dislocations. The silicondioxide isolation regions 24 may be formed using one of the methodsdisclosed herein.

In the processes described above, a strained silicon or silicongermanium layer is able to be fabricated on or over a relaxed silicongermanium buffer layer grown on or over a silicon substrate. Devices maythen be fabricated in the regions 20 b of the strained silicon orsilicon germanium layer. The threading dislocations may be formed orforced into the isolation regions 24. Consequently, there is effectiveuse of the available “real estate” of the substrate 2 for devicefabrication. On a surface area basis, the non-damaged portion of thesubstrate 2 (where device fabrication can occur) may exceed 98%. Thus,substantially the entire surface of the substrate 2 may be formedsubstantially free of threading dislocations.

FIGS. 27A, 27B, and 27C illustrate a process of forming an array ofquantum dots 40 on a substrate 42 (e.g., a silicon substrate 42). Asubstrate 42 may be provided and a strained silicon germanium layer 44may be grown or otherwise deposited on or over the substrate 42. Usingthe methods described herein, regions 44 a of the strained silicongermanium layer 44 may be irradiated with a dislocation inducing agent 8(not shown in FIGS. 27A, 27B, and 27C). The regions 44 a may include anarray of points (as is shown in FIG. 27) or may include an intersectingnetwork of lanes. As seen in FIG. 27B, the substrate 42 and strainedsilicon germanium layer 44 may then subject to an annealing process torelax the strain in the silicon germanium layer 44. A layer of relaxedsilicon germanium 45 may be formed. A relaxation process forms adislocation network 46 (e.g., a substantially perpendicular network)that includes misfit dislocation segments 48 that interconnect with thedamaged regions 44 a shown in FIG. 27A.

As seen in FIG. 27C, a regular array of quantum dots 40 may be grown onthe relaxed silicon germanium layer 45. The quantum dots 40 may then bepreferentially formed on the dislocation network 46.

While particular embodiments have been shown and described, variousmodifications may be made without departing from the scope of theclaimed subject matter. The claimed subject matter, therefore, shouldnot be limited, except to the following claims, and their equivalents.

1. A method for controlling a dislocation position in a silicongermanium buffer layer, comprising: depositing a strained silicongermanium containing layer on a substrate; forming a silicon cappinglayer over the strained silicon germanium layer; irradiating the silicongermanium containing layer with a dislocation inducing agent so as toirradiate a plurality of intersecting lanes generally arrangedperpendicular to one another; transforming the strained silicongermanium containing layer into a relaxed state; and whereindislocations in the silicon germanium containing layer are located inthe plurality of intersecting lanes.
 2. The method of claim 1, furthercomprising depositing a layer of strained material selected from thegroup consisting of strained silicon and strained silicon germanium onthe relaxed silicon germanium containing layer.
 3. The method of claim2, further comprising exposing the one or more regions containing thedislocations with a mask disposed on the layer of strained material; andforming silicon dioxide isolation regions in the plurality ofintersecting lanes containing the dislocations.
 4. The method of claim3, wherein the silicon dioxide isolation regions are formed by oxygenion implantation followed by an annealing process.
 5. The method ofclaim 1, wherein the dislocation inducing agent comprises ions.
 6. Themethod of claim 1, wherein the dislocation inducing agent compriseselectrons.
 7. The method of claim 1, wherein the width of theintersecting lanes is greater than the critical radius of dislocationloops formed therein.
 8. A method for controlling a dislocation positionin a silicon germanium buffer layer, comprising: depositing a strainedsilicon germanium containing layer on a substrate; forming a siliconcapping layer over the strained silicon germanium layer; irradiating thesilicon germanium containing layer with a dislocation inducing agent soas to irradiate a plurality of lanes oriented in a first direction;annealing the substrate and silicon germanium layer; irradiating thesilicon germanium containing layer with a dislocation inducing agent soas to irradiate a plurality of lanes oriented in a second directionwhich is substantially perpendicular to the first direction; andannealing the substrate and silicon germanium layer.
 9. The method ofclaim 8, further comprising depositing a layer of strained material onthe relaxed silicon germanium containing layer wherein the strainedmaterial is selected from the group consisting of strained silicon andstrained silicon germanium.
 10. The method of claim 9, furthercomprising exposing the plurality of lanes with a mask disposed on thelayer of strained material; and forming silicon dioxide isolationregions in the plurality of lanes containing the dislocations.
 11. Themethod of claim 10, wherein the silicon dioxide isolation regions areformed by oxygen ion implantation followed by an annealing process. 12.The method of claim 8, wherein the dislocation inducing agent comprisesions.
 13. The method of claim 8, wherein the dislocation inducing agentcomprises electrons.
 14. The method of claim 8, wherein the width of theintersecting lanes is greater than the critical radius of dislocationloops formed therein.
 15. A method of forming a relaxed silicongermanium buffer layer, comprising: depositing a strained silicongermanium containing layer on a substrate; forming a silicon cappinglayer over the strained silicon germanium layer; forming a mask on thesilicon capping layer; irradiating exposed portions of the silicongermanium containing layer underlying the silicon capping layer with adislocation inducing agent to produce dislocation loops in theirradiated portions to form a dislocation network; and annealing thesubstrate and silicon germanium layer so as to propagate an intersectingnetwork of misfit dislocation segments.
 16. The method of claim 15,further comprising depositing a layer of strained material on therelaxed silicon germanium containing layer wherein the strained materialis selected from the group consisting of strained silicon and strainedsilicon germanium.
 17. The method of claim 15, further comprisingforming silicon dioxide isolation regions in the intersecting network ofmisfit dislocation segments.
 18. The method of claim 1, wherein thestrained silicon germanium containing layer is transformed into arelaxed state by subjecting the substrate and strained silicon germaniumcontaining layer to an annealing process.